Peter Capaldi as Malcolm Tucker in The Thick Of It. Photograph: Mike Hogan/BBC

SPOILER ALERT: This weekly blog is for those who are watching The Thick of It series three. Don't read on if you haven't seen episode seven

The king is dead. Long live the king?

Throughout this series Malcolm Tucker (Peter Capaldi), the government's press chief, has spun further and further out of control.

A couple of weeks ago, his opposite number, Stewart Pearson, responded to one characteristic rant (the one about tracking down and murdering a radio phone-in caller) by saying Malcolm sounded "quite mad". The note of pity in his voice was as damning as the jibe itself. Last week hapless departmental press officer Terri Coverley took him to task – rightly – for flaws in his PR strategy.

And this week an old nemesis from Malcolm's past returns: Steve Fleming (David Haig), the PM's fixer, who Malcolm once drummed out of the party. Special adviser Ollie Reeder calls him "the man who brought us back into power", which perhaps identifies him as a Mandelson figure, but with his sinister fake charm and disgusting moustachioed grin Fleming has none of the business secretary's Morrissey-esque wit or grace.

His return worries Malcolm enough for him to invite several top journalists to dinner at his house to impress upon them that he is still in charge, although typically he pretends he has gathered them there as a favour: "I know that these are hard times for print journalists. I mean, I read that, on the internet." Is he threatened by Fleming? "This is about a guy sharing his ghee – that's it."

This was a very sharp episode, the first half consistently funny, with banter and insults zinging from one side of the court to the other like volleys from Andy Murray, whose name was taken in vain throughout. The programme's switches in tone have been awkward recently, but the last 10 minutes of tonight's episode, as it made a gradual swerve into serious drama, were genuinely tense and chilling.

The descent began with an ominous cameo from another of Malcolm's old sparring partners, the blue-skies thinker Julius – now Lord – Nicholson (Alex McQueen), who seems to be partly based on Lord "more Andrew than" Adonis, the transport secretary. The last scenes during which Fleming sneered his final lines of triumph, Malcolm's BlackBerry stopped working, and his career crashed to a halt on a TV screen behind him were fantastically brutal, although I was taken aback by all the cheering, hugging and drinking wine among the staff. I think I would have been more with Glenn: "It feels good, but is it good?"

What are we to make of Malcolm's final threat: "You will see me again! You will fucking see me again." Will he use the media that he was once so adept at handling to try to bring the PM down from outside the government? The next series of The Thick of It will almost certainly centre on opposition characters such as the brilliant Peter Mannion MP. Is it remotely plausible that Malcolm could cross the floor?

I hope not. The Thick of It is at its best when it mirrors real life. Malcolm Tucker worked so well as a character because he represented that aggressive, ultra-macho style of politics typified by Alastair Campbell, Damian McBride, Ed Balls and others. Although David Cameron has a snarling former tabloid editor as his press chief (Andy Coulson), this is far from the default mode of the government-in-waiting. The era of Campbell/Tucker has already come to a close.

Far better for Armando Iannucci and the other writers to take stock of the Cameron government when it arrives and write a series of The Thick of It that has something to say about the new politics sure to be ushered in after the next general election. Malcolm Tucker is now old news – as the last few episodes have shown. As this series closes next week, Malcolm should bow out too.

Best swearing

"Andy Murray's Henman-fisting us in the press." - Malcolm. Is that swearing? It's pretty rude.